It is known to provide a traveling body such as a large suitcase, a luggage carrier, various wagons, and the like with four caster wheels mounted on the lower surface thereof so as to be positioned at the four corners thereof. If these four wheels are all designed to be swiveled freely, the traveling direction will not be fixed, whereas if all the wheels are restrained from swiveling, it will difficult to move the body in a curved fashion. It is therefore desirable for the two wheels that are forward relative to the traveling direction to be free to swivel and the two wheels that are rearward to be restrained from swiveling. However, it has been impossible for conventional caster devices to provide the wheel states as mentioned above, regardless of the traveling direction, merely by changing the traveling direction of the traveling body without performing any operation.
The present inventor has proposed a caster device which can meet the requirements as described hereinbefore. Namely, his Laid-open Japanese Patent Application No. 55-156702 discloses a caster device in which the swivel shaft of the wheel is provided integrally with a supporting frame of the wheel, the swivel shaft being rotatably supported on a base housing, an engaging element and a locking member having a locking portion which engages the engaging element to restrain the rotation of the swivel shaft are provided on the side of the swivel shaft and the side of the base housing, respectively, and the engaging element and the locking portion of the locking member are engaged or disengaged responsive to the urging of the engaging element resulting from the swiveling force of the supporting frame so that the changeover between the free state and restrained state of the wheel may be effected by changing the moving direction of the wheel. According to this caster device, it is always possible to freely swivel the two front wheels and to restrain the swiveling of the two rear wheels, irrespective of the traveling direction of the traveling body. However, in the case the traveling body has a great weight or in the case the traveling body is loaded with heavy articles, the aforesaid engaging element is apt to become disengaged from the locking portion of the locking member due to the traveling inertia resulting from said weight, thus giving rise to the situation that the swiveling of the rear wheels may not be restrained.